datapkg_read() - support loading from zipped Data Package

[danfowler]

Feedback from pilot partner on trialling this package:

Otherwise if I need to unzip the package, it loses the "neatness" of having everything in one file.

Support loading a zipped Data Package. This is currently supported by the datapackage-py Python implementation:

https://github.com/frictionlessdata/datapackage-py/blob/master/datapackage/datapackage.py#L26